Ethereum address validation and normalization in Ruby

eth.rb

# Extracted from https://github.com/se3000/ruby-eth
#
# Dependencies:
# - gem 'digest-sha3'
# - gem 'rlp'
#
# Usage:
# - Eth::Utils.valid_address?('0x4Db7569F90bd836294B11c8b08B853d2de499Ced')
#   => true
# - Eth::Utils.format_address('0x4db7569f90bd836294b11c8b08b853d2de499ced')
#   => 0x4Db7569F90bd836294B11c8b08B853d2de499Ced

module Eth
  module Utils
    extend self

    def prefix_hex(hex)
      hex.match(/\A0x/) ? hex : "0x#{hex}"
    end

    def bin_to_hex(string)
      RLP::Utils.encode_hex string
    end

    def remove_hex_prefix(s)
      s[0,2].downcase == '0x' ? s[2..-1] : s
    end

    def keccak256(x)
      Digest::SHA3.new(256).digest(x)
    end

    def valid_address?(address)
      Address.new(address).valid?
    end

    def format_address(address)
      Address.new(address).checksummed
    end
  end

  class Address
    def initialize(address)
      @address = Utils.prefix_hex(address)
    end

    def valid?
      if !matches_any_format?
        false
      elsif not_checksummed?
        true
      else
        checksum_matches?
      end
    end

    def checksummed
      raise "Invalid address: #{address}" unless matches_any_format?

      cased = unprefixed.chars.zip(checksum.chars).map do |char, check|
        check.match(/[0-7]/) ? char.downcase : char.upcase
      end

      Utils.prefix_hex(cased.join)
    end

    private

      attr_reader :address

      def checksum_matches?
        address == checksummed
      end

      def not_checksummed?
        all_uppercase? || all_lowercase?
      end

      def all_uppercase?
        address.match(/(?:0[xX])[A-F0-9]{40}/)
      end

      def all_lowercase?
        address.match(/(?:0[xX])[a-f0-9]{40}/)
      end

      def matches_any_format?
        address.match(/\A(?:0[xX])[a-fA-F0-9]{40}\z/)
      end

      def checksum
        Utils.bin_to_hex(Utils.keccak256 unprefixed.downcase)
      end

      def unprefixed
        Utils.remove_hex_prefix address
      end
  end
end